1. Field of the Invention
The present invention relates to an image display system for displaying an image on the basis of an image signal sent from a computer, and an image display device.
2. Description of the Background Art
FIG. 8 is a block diagram showing a configuration of a conventional image display system. As shown in FIG. 8, the conventional image display system is provided with a computer system 100 and a display device 110 connected to the computer system 100. The display device 110 has a preamplifier 120, an analog/digital converter (hereinafter, referred to as “A/D converter”) 130, a microcomputer 140, a PLL (Phase Locked Loop) unit 150, a graphic controller 160 and a liquid crystal display panel 170.
The computer system 100 outputs an analog image signal composed of color signals of red (R), green (G) and blue (B) to the preamplifier 120, and outputs a horizontal synchronous signal H and a vertical synchronous signal V to the microcomputer 140. The preamplifier 120 adjusts the signal level of the received analog image signal on the basis of control of the microcomputer 140, and outputs the analog image signal having the adjusted signal level to the A/D converter 130. Hereinafter, the analog image signal to be inputted to the preamplifier 120 is referred to as “input analog image signal” and the analog image signal to be outputted from the preamplifier 120 is referred to as “output analog image signal”.
The A/D converter 130 converts the received output analog image signal to a digital image signal on the basis of a sampling clock outputted from the PLL unit 150, and outputs the resulting signal to the graphic controller 160. Further, the microcomputer 140 detects and separates the horizontal synchronous signal H and vertical synchronous signal V outputted from the computer system 100, identifies the operation mode on the basis of the frequencies of the separated horizontal synchronous signal H and vertical synchronous signal V, and recognizes the resolution which corresponds to the operation mode. Moreover, the separated horizontal synchronous signal H and vertical synchronous signal V are outputted to the PLL unit 150 and the graphic controller 160.
The PLL unit 150 variably changes the sampling clock in accordance with the resolution recognized by the microcomputer 140, and outputs the resulting sampling clock to the A/D converter 130. The graphic controller 160 adjusts the frequency of the digital image signal outputted from the A/D converter 130 in accordance with the resolution recognized by the microcomputer 140, and displays an image on the liquid crystal display panel 170.
Then, an adjusting process of the signal level of an input analog image signal that is carried out in the preamplifier 120 will be described in detail. In the above-described conventional image display system, in order to appropriately carry out the gradation-display of an image, it is necessary to carry out a gradation adjustment of making the signal level of the output analog image signal coincident with the analog input range of the A/D converter 130. This gradation adjustment is carried out in the preamplifier 120. Here, the “analog input range” means a range of the analog signal level for which the A/D converter 130 can output a digital signal in accordance with the signal level of the analog signal when the A/D converter 130 converts an analog signal to a digital signal. Therefore, analog signals exceeding this range are outputted from the A/D converter 130 as digital data having a constant value regardless of the signal level.
More specifically, on the basis of the control of the microcomputer 140, the preamplifier 120 amplifies the amplitude of the input analog image signal. By varying the value of the minimum level (hereinafter, referred to as “bias value”) of the input analog image signal with respect to a reference voltage, e.g., 0V, the signal level of the output analog image signal is made coincident with the analog input range of the A/D converter 130. In other words, on the basis of the control of the microcomputer 140, the preamplifier 120 adjusts the amplification rate (hereinafter, referred to as “gain value”) and the bias value of the input analog image signal. The microcomputer 140 stores a program (hereinafter, referred to as “program for adjustment”) used for adjusting the gain value and bias value of the input analog image signal. This program is executed by the microcomputer 140 so that the gain value and bias value of the input analog video signal are set.
Next, a setting method of the gain value and bias value of the input analog image signal in a conventional image display system will be described in more detail. FIG. 9 is a flow chart showing the setting method of the gain value and bias value of the input analog image signal in the conventional image display system. As shown in FIG. 9, at step ST100, the gain value and the bias value are initialized.
Next, at step ST110, a base address register is set, which is used for reading data of the digital image signal (hereinafter, referred to as “stable area data”) corresponding to a stable area of the black area in the input analog image signal which is inputted so as to adjust the bias value. Then, at step ST120, a judgment is made as to whether or not the value of the stable area data read out through the base address register thus set is greater than the minimum value “00” of the digital output range of the A/D converter 130. Here, the “stable area” means an area which is not subjected to influences from a ringing phenomenon which tends to generate in edge portions of the input analog image signal, and is specified by a program for adjustment installed in the microcomputer 140. Moreover, the stable area data, which is read out through the base address register, is data set on a pixel basis.
As a result of the judgment at step ST120, when the value of the stable area data, which is read out through the base address, is greater than the minimum value of the digital output range of the A/D converter 130, the bias value is reduced at step ST130, and at step ST120, the judgment is again made as to whether or not the value of the stable area data read through the base address is greater than the minimum value of the digital output range of the A/D converter 130. As a result of the judgment at step ST120, when the value of the stable area data, which is read out through the base address, is equal to the minimum value “00” of the digital output range of the A/D converter 130, the adjusting process of the bias value is completed at step ST140.
Upon completion of the adjustment of the bias value, at step ST150, a base address register is set, which is used for reading the stable area data of the white area in the input analog image signal which is inputted so as to adjust the gain value. Then, at step ST160, a judgment is made as to whether or not the value of the stable area data read out through the base address register thus set is smaller than the maximum value “FF” of the digital output range of the A/D converter 130.
As a result of the judgment at step ST160, when the value of the stable area data, which is read out through the base address, is smaller than the maximum value of the digital output range of the A/D converter 130, the gain value is increased at step ST170, and at step ST160, the judgment is again made as to whether or not the value of the stable area data, which is read through the base address, is smaller than the maximum value of the digital output range of the A/D converter 130. As a result of the judgment at step ST160, when the value of the stable area data, which is read out through the base address, is equal to the maximum value of the digital output range of the A/D converter 130, the adjusting process of the gain value is completed at step ST180.
As described above, in the conventional image display system, a stable area, which is not subjected to influences from a ringing phenomenon in the input analog image signal, is used so as to set the gain value and bias value of the input analog image signal. Then, a gradation adjusting process, which makes the signal level of the output analog image signal coincident with the analog input range of the A/D converter 130, is carried out. Thus, it becomes possible to carry out an appropriate gradation displaying process.
With respect to the conventional image display system as described above, Japanese Patent Application Laid-Open No. 2001-13931 discloses substantially the same arrangement.
However, in the above-described conventional image display system, since the stable area varies depending on the computer system 100 to be connected to the display device 110, the stable area specified by the program installed in the microcomputer 140 sometimes corresponds to an area which is subjected to influences from a ringing phenomenon. In such a case, the stable area data, which is read out through the base address register, is also subjected to influences from a ringing phenomenon. In addition, the stable area data, which is read out through the base address register, is set on a pixel basis, so that processes at steps ST120 to ST140 or steps ST160 to ST180 are executed on a pixel basis. In other words, the gradation adjusting process is carried out by using stable area data corresponding to only one pixel. Therefore, depending on the computer system 100 to be connected to the display device 110, the gain value and bias value of the input analog image signal are set by using only the stable area data which has been subjected to influences from a ringing phenomenon, resulting in a failure to carry out an appropriate gradation displaying process in some cases. This makes it impossible to provide appropriate image quality to the user.
Moreover, in order to provide appropriate image quality to the user, with respect to adjustments of image quality, not only a gradation adjustment of making the signal level of the output analog image signal coincident with the analog input range of the A/D converter 130, but also adjustments on luminance and γ-characteristic need to be carried out.